Apparatus for uniformly distributing fluid through a bed of particulate material

ABSTRACT

Apparatus for uniformly distributing a fluid such as a vapor or gas upwardly through a cylindrical bed of a particulate contact material such as a catalyst, without interfering with the catalyst flow, includes an annular chamber which is closed at its top and which surrounds the cylindrical bed. The annular chamber receives fluid near its top and distributes it evenly at its bottom where it passes the fluid downwardly into a region which contains catalyst particles which have descended from the cylindrical bed, said region being defined at its top by the catalyst at the bottom of the aforesaid cylindrical bed and the open bottom end of the annular chamber, at its bottom by the bottom of a vessel containing the apparatus, and at its sides by the sides of the vessel. The distance between the bottom of the cylindrical bed and the bottom of the vessel is preferably at least equal to the radius of the cylindrical bed.

BACKGROUND OF THE INVENTION

The invention relates to apparatus of the type wherein a fluid such as agas or vapor is used to react with or treat a particulate type ofcontact material such as a catalyst, which is passing by gravity fromone reaction or treating zone to another. Examples of processes carriedout in such an apparatus include various hydroprocessing techniques suchas catalytic reforming, catalyst regeneration, hydrotreating,dehydrogenation of butane and dehydrocyclodimerization, to name a few. Aspecific example of a catalyst regeneration apparatus in which acatalyst whose surface has been covered with coke during a catalyticreforming operation, moves downward through a carbon burnoff section,through a halogenation section and into a drying section is shown anddescribed in Greenwood et al., U.S. Pat. No. 3,652,231, the subjectmatter of which is herein incorporated by reference. In the embodimentof FIG. 3 of the referenced patent, the catalyst moves downwardly in theannular space between a pair of spaced concentric perforated screens andis subjected initially to a first radially flowing recycle flue gashaving a relatively low oxygen content and secondly, to a radiallyflowing second gas containing air, a halogen and steam. The catalystcontinues to move from the aforesaid annular space as a descending bedinto a generally cylindrical drying section wherein it is contacted by ahot and dry air stream, or other suitable drying medium before it exitsthe bottom of the apparatus. The drying medium is typically distributedby an arrangement of perforated distributor members including a centraltrunk with a plurality of laterally extending branches positionedgenerally uniformly in a horizontal plane near the bottom of the dryingsection. In order to minimize plugging of the distributor members by thecatalyst particles, the distributor members usually have their flowopenings located only in their downwardly facing portions. However, evenwhen the distributor members are intricately fabricated so as to includespaced apart wedge wire screen portions which form slots in their bottomsurfaces and internal baffles to help distribute the flow uniformlythrough all of the slots, it appears that plugging of the distributorsis still possible. Also, since plugging of a few slots produces highervelocities at the other slots, the plugging becomes progressivelygreater since the higher velocities can produce unwanted fluidizationand consequent catalyst attrition which can cause additional plugging.The placing of a large number of branch pipes or laterals on adistributor pipe can permit lower flow velocities, and thus less chanceof damaging fluidization, than where fewer branches are present.However, the mere presence of any pipes in the catalyst bed produces anobstruction in the downward flow path of the catalyst bed which canaccelerate attrition and, of course, a greater number of pipes wouldincrease the problem. In addition to the attrition caused to thecatalyst when gas velocities become too large due to screen plugging,the use of perforated distributor members is also very costly,especially when such members must be fabricated from sections of slottedscreens.

SUMMARY

It is among the objects of the present invention to provide an apparatusfor distributing fluid upwardly through a generally cylindrical bed ofparticulate material that results in more uniform flow distribution thanexisting devices, that is simple and relatively inexpensive to produce,and which is incapable of being plugged.

It is another object of the invention to provide a fluid distributionapparatus that will not interfere with the downward plug flow of a bedof particulate material inside a generally cylindrical vessel.

Yet another object is to provide an apparatus for distributing fluidupwardly through a generally cylindrical bed of contact material whichcan be adapted for use in existing vessels which were initially designedfor conventional perforated pipe distributors.

The foregoing and other objects and advantages are attained by thedistribution apparatus of the present invention in which a flow offluid, generally a vapor, is brought into an upper part of an annularchamber which surrounds a generally cylindrical member containing a bedof particulate material to be contacted by the fluid. The bed ispreferably moving downwardly but could also be fixed. The annularchamber is sealed at its top but open at its bottom. In a preferredembodiment for achieving extremely uniform flow through the bed ofparticulate material, the wall portion of the vessel which defines theouter wall of the aforesaid annular chamber extends downwardly from theannular chamber until it meets a bottom wall of the vessel. The catalystin the vessel has a vertical cross-section defined by the bottom wall ofthe vessel, the downward extension of the outer wall of the annularchamber and the inner wall of a tubular member whose outer wall definesthe inner wall of the annular chamber. The diameter of the verticalcatalyst cross-section is greater in the region immediately below theannular chamber than it is in the region which is immediately adjacentthe inner wall of the tubular member. Also, the height of the catalystcross-section in the region below the tubular member, as measuredbetween the bottom edge of the tubular member that defines the innerwall of the catalyst chamber and a point on the bottom wall which isvertically aligned with the tubular member, is substantially no less,and preferably at least equal in dimension to the radius of the saidtubular member.

Where space constraints are especially tight, such as when it is desiredto modify an existing vessel in which the fluid inlet for the fluid tobe distributed is located relatively close to the bottom of the vessel,it is possible to have the height of the catalyst cross-section beneaththe tubular member somewhat less than the radius of the tubular member.In such a modification, the flow distribution of the fluid will not beas uniform across the entire catalyst bed within the tubular member, atleast near the bottom of the tubular member, as in the preferredarrangement. However, the distribution can be significantly better thanwith distributor pipe arrangements, and will result in less attrition.Where space constraints also limit the vertical dimension of the annularchamber between the fluid inlet port and the surface of the catalyst bedwhich is located at the bottom of the annular chamber, it is desirableto install an annular perforated ring in the chamber. The perforatedring, when appropriately perforated, will produce a backpressure on thefluid and thereby cause the fluid to exit the annular chamber uniformlyaround its entire circumference, even though the fluid enters theannular chamber through a single inlet port. In order to calculate thepressure drop to be provided by the annular ring for a specific examplevessel which it was desired to modify, and to determine the size of theholes to be used in the annular ring, the pressure drop was firstcalculated, without a ring being present, between the fluid inlet and apoint 180° away on the opposite side of the vessel. The pressure drop tobe provided by the annular plate was then calculated to be equal toabout 10 times the previously calculated pressure drop. Finally, theflow velocity at a specific distance below the annular ring wascalculated for a number of different size holes that would produce thecalculated pressure drop. For example, for a particular desired pressuredrop across the annular perforated plate, it was determined that the useof 0.125" diameter holes would produce a velocity of 5 fps at a distanceof 10 inches below the annular plate. Similarly, holes of 0.1875" wouldproduce a velocity of 7 fps, holes of 0.250" would produce a velocity of10 fps, and holes of 0.375" would produce a velocity of 14 fps. Theparticular size of holes to be used can then be selected based upon themaximum velocity of flow which the designer desires to apply to thecatalyst or other particulate matter. Preferably, the flow velocity ismaintained below the velocity at which the particulate matter will startto fluidize, since fluidization produces attrition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-section of the cylindrical drying section ofa continuous catalyst regeneration tower which incorporates theinvention in its preferred mode;

FIG. 2 is a schematic representation, based on a computer model, of theflow of vapor down into and up through one half of a cylindricalcatalyst bed;

FIG. 3 is a vertical cross-section of a modification of the inventiondisclosed in FIG. 1 which can be utilized where vertical space is at apremium, such as in the replacement of an existing perforated pipe typeof distributor apparatus; and

FIG. 4 is a fragmentary top plan view of a perforated annular ring whichis shown in vertical section in FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, the invention is illustrated in association with asection of a cylindrical catalyst regeneration tower indicated generallyat 10, which is part of a continuous catalytic reformer. The towersection illustrated includes an upper halogenation zone indicatedgenerally at 12 and a lower drying zone indicated generally at 14. Theflow path of the vapor entering inlet port 16 in the upper zone 12extends principally in a radial direction through the annular bed 20 ofcatalyst particles 22 which is descending downwardly between theperforated screen members 24, 26. However, a very small portion of thevapor from port 16 exits downwardly between the non-perforated lower end26' of the screen 26 and the outer vessel wall 30 and then passesupwardly into the open region 32. The annular bed 20 passes downwardlyinto, and fills, a generally cylindrically shaped chamber 34 defined bythe inner wall of a pipe member 36 whose upper end tapers outwardly as acone-shaped portion 38 until it contacts and is welded to the outervessel wall 30. Since the annular catalyst bed 20 gravitationally entersthe chamber 34 at the upper end of cone-shaped portion 38, the uppersurface of the catalyst bed 40 will assume the generally conical surfaceindicated at 40'. As discussed in detail in my co-pending U.S.application Ser. No. 686,053, filed Dec. 24, 1984, now U.S. Pat. No.4,567,022, which is assigned to a common assignee and issued on Jan. 28,1986 as U.S. Pat. No. 4,567,022, the aforedescribed structure preventsany of the vapors normally passing upwardly through bed 40 fromcontacting the catalyst near the bottom of bed 20. Thus, it is feasibleto sample such catalyst through a sampling port such as the one shown at44.

The present invention is principally concerned with distributing a vaporor gas which enters the drying zone 14 through a port 48 in the outervessel wall 30 in such a manner that it can pass upwardly through thecatalyst bed 40 contained in the generally cylindrical chamber 34 in avery uniform manner and without in any way obstructing the downwardmovement of the bed 40. The inside diameter of the pipe member 36 andthe minimum vertical height of the catalyst bed 40 located above theplane containing the bottom end 36' of the pipe member 36 generallydetermine the volume of catalyst to be contacted by the vapor or gasentering port 48. By controlling the average volume of catalyst beingremoved per unit of time through the lower exit ports 52, the residencetime of contact between the catalyst and the vapor or gas can becontrolled. It is important that the diameter of the pipe member 36 notbe too small since decreasing the diameter of chamber 34 would cause acorresponding increase in the velocity at which a predetermined volumeof vapor or gas entering port 48 impinges on the catalyst particles. Asis well known, too great an infringement velocity will tend to fluidizethe particles of the bed and cause them to attrite. Where the vapor orgas enters the open annular chamber 60 between the pipe member 36 andthe vessel wall 30 at a single location, such as port 48, it isdesirable to place the port 48 at a relatively high position in thechamber 60. It should be located far enough above the lower end 36' ofthe pipe member 36 that the incoming vapor or gas will becomesufficiently well distributed in the chamber 60 that it will exit at arelatively uniform velocity and flow rate around the entire periphery ofthe lower end 36' of the pipe member. A position for the port 48 whichis equal to five or more radial widths of the chamber 60 appears toprovide satisfactory results. It is also desirable that a point 72 onthe bottom wall 64 of the vessel which is located in vertical alignmentwith the lower end 36' of the pipe member be spaced from end 36' by adistance "x" which is substantially no less than, and preferably equalto or greater than, the radius "y" of the pipe member 36. The distance"x" should be sufficient to allow the vast majority of the downward flowof vapors or gases exiting the annular chamber 60 to pass through thelower catalyst bed portion 40" substantially without obstruction and bedistributed substantially uniformly across the entire transversecross-section of the catalyst bed portion 40. Although dimension "x" isshown in FIG. 1 as being substantially greater than dimension "y", theprincipal reason for this difference is to establish plug flow ofcatalyst in bed 40 above lower edge 36' of chamber 34. Cone shapedcovers 68 located above exit ports 52 aid in establishing theabovementioned plug flow.

FIG. 2 is a schematic representation generated from a computer model,illustrating the flow streamlines for equal volumes of vapor entering acylindrical particulate catalyst bed 140 from an annular chamber 160.The elements numbered 130-164 in FIG. 2 correspond to the similarelements 30-64 in FIG. 1. To illustrate the uniformity of the flowachieved, the radius "r" of the pipe member 136 or catalyst bed 140 isdivided into five segments "a", "b", "c", "d", and "e" which are of adimension such that the circular or annular areas which underlie themwill all be equal in area. The nineteen streamlines 170 which are shownin FIG. 2 divide the vapor flow entering the catalyst beds 140", 140into twenty equal volumes. Since each of the segments of "a"-"e" is seento contain four streamlines, it is obvious that uniform contact will beachieved with all of the catalyst particles which make up bed 140. Itcan be further seen that the uniformity of flow is achieved quite nearthe bottom of the bed 140 since the streamlines 170 appear to quicklybecome vertical after they enter bed 140. To obtain the character ofuniform distribution shown in FIG. 2, it is preferable to have the lowercatalyst bed 140" deep enough that a point 172 on the bottom wall 164 ofthe vessel which is in vertical alignment with the pipe member 136 willbe positioned below the lower edge of pipe 136 by a distance "h" whichis at least equal to the radial dimension "r".

FIG. 3 is a vertical cross-sectional view illustrating a modification ofthe flow distributor invention disclosed in FIG. 1. The apparatusindicated generally at 210 represents a modification of an existingregenerator vessel 230 in which the vapor or gas inlet port 248 islocated far closer to the bottom wall 264 of the vessel than is the casewith the corresponding elements 48, 64 in FIG. 1. Before modification,the catalyst bed 240 would have extended to the outer walls of thevessel 230 and the vessel would have lacked the pipe member element 236and surrounding ring 276. There would also have been a central trunk ofa pipe distributor, and several branches, projecting across the interiorof the vessel from port 48. To modify the existing vessel, the old pipedistributor (not shown) is removed and a pipe member 236 is installed bywelding its tapered top portion 238 to the outer wall of the vessel 230.The diameter selected for the pipe member 236 is somewhat critical sinceit must be large enough that the quantity of gas passing upwardlythrough the catalyst bed 240 will have a velocity below the fluidizationvelocity of the catalyst bed. However, increasing the diameter of pipe236 would obviously decrease the radial width of the annular chamber260. Since a given volume of gas must exit downwardly from annularchamber 260 into catalyst bed portion 240", it is also necessary thatthe annular cross-sectional area of chamber 260 be large enough toinsure that the gas will not fluidize the catalyst particles as itenters bed portion 240". In the configuration shown in FIG. 3, thesingle gas inlet port 248 is shown as being positioned so close to thebottom edge 236' of the pipe member 236 that one could not normallyexpect to achieve a uniform volume of flow around the entirecircumference of the annular lower end of the chamber 260. However, bypositioning an annular ring 276 having a plurality of perforations 276'(FIG. 4) intermediate the inlet port 248 and the bottom of pipe member236, it is possible to create sufficient backpressure that the gasentering port 248 will be uniformly distributed by the time it reachesthe catalyst bed 240". As previously discussed, the diameter of theperforations is selected for a given pressure drop across the annularperforated ring 276, to provide a particular velocity at a predetermineddistance below the ring. A large number of small holes will obviouslyprovide a lower maximum gas velocity at any point located in a plane ata predetermined distance below the ring than a smaller number of largerholes since the flow from the more closely positioned holes will blendtogether in a shorter distance.

In the embodiment shown in FIG. 3, it is apparent that the verticaldistance between the lower edge 236' and a point 272 on the lower endmember 264 which is immediately beneath the edge 236' is slightly lessthan the radius of chamber 34. Although such a situation could result inslightly less uniform flow distribution than if the said verticaldistance were equal to or greater than the chamber radius, as in FIG. 1,the distribution would still be far superior to that achieved by theprior art pipe distributors.

I claim:
 1. Apparatus for contacting a gas with a bed of particleswherein: (1) there is no obstruction to downward movement of particlesthrough said bed, (2) flow of said gas through any horizontalcross-section of said bed is substantially uniform, and (3)substantially all of said gas passes through the entire vertical heightof said bed, said apparatus comprising:(a) a vertical cylindrical pipemember which contains said bed; (b) a sidewall section of a verticalcylindrical vessel and an internal partition disposed in a generallyhorizontal manner within said sidewall section, where said sidewallsection is larger in diameter than said pipe member, where the pipemember is coaxially disposed within said sidewall section, where thesidewall section extends below the lower end of the pipe member, andwhere particles leaving the lower end of said bed are contained by saidsidewall section and partition such that there is no discontinuity inthe mass of particles occupying the bed and the sidewall section belowthe pipe member; (c) an annular chamber formed by the outer surface ofsaid pipe member and the inner surface of said sidewall section; (d) apartition disposed between the top of the pipe member and the sidewallsection in order to prevent gas from flowing out of the top of saidannular chamber; and, (e) at least one gas inlet port in said sidewallsection which is spaced vertically above the lower end of the pipemember.
 2. The apparatus of claim 1 further characterized in that thevertical distance between the bottom end of the pipe member and saidpartition is at least equal to the radius of the pipe member.
 3. Theapparatus of claim 1 further characterized in that the vertical distancebetween the bottom of the pipe member and the centerline of said gasinlet port is equal to at least five times the radial width of theannular chamber.
 4. The apparatus of claim 1 further including ahorizontal annular ring member having a plurality of perforations, whichring member is sealingly disposed in the annular chamber between the gasinlet port and the bottom of the pipe member such that gas flowingdownward in the annular chamber must pass through said perforations,where said perforations are sized and distributed around thecircumference of said ring member such that the downward flow of gas inthe annular chamber below the ring member through any horizontal crosssection is substantially uniform.
 5. The apparatus of claim 1 furthercharacterized in that said particles are particles of catalyst and saidbed comprises a drying zone of a catalyst regeneration section of acontinuous catalytic reforming unit.